Circulation process and device in sulphite cellulose digestion



Nov. 20, 1934. s. svENssoN CIRCULATION PROCESS AND DEVICE IN SULPHITE CELLULOSE DIGESTION Filed Nov. 10, 1952- 4 Sheets-Sheet 1' SV'NSSM I Nvelv TaR NOV. 20, 1934. s $VEN$$QN 1,981,759 CIRCULATION PROCESS AND DEVICE IN SULPHITE C'ELLULOSE DIGESTION Filed No v. 10,- 1932 4 Sheets-Sheet 2 sve xlssm INVGN Fa/Q Nov. 20, 1934. ENS ON 1,981,759

CIRCULATION PROCESS AND DEVICE IN SULPHITE CELLULOSE DIGESTION Filed Nov. 10, 1932 4 Sheets-Sheet 5 |U 0 W uni a 52 Nov. 20, 1934. s. SVENSSONV 1,981,759

CIRCULATION PROCESS AND DEVICE IN SULPHITE CELLULOSE' DIGESTICN Filed Nov. 10, 1932 4 Sheets-sheaf 4 5. Svewssm v IvveN MR BY; W $64k PHM ' Patented Nov. 20, 1934 PATENT OFFICE,

CIRCULATION PROCESS AND DEVICE IN SULPHITE CELLULOSE DIGESTION Sjune Svensson, Hissmofors, Krokom, Sweden Application November 10, 1932, Serial No. 642,112 In Sweden October 22, 1931 Claims.

The present invention relates to improvements in and relating to digestion of fibrous material for the production of sulphite cellulose and other similar digestion processes, and particularly proci esses which are adapted to effect circulation of the digesting liquid in such digestion.

It has appeared that a uniform degree of attack of the digested fibrous material is obtained only when the circulating digesting liquid is drawn off i in the lower portion of the digester, and is introduced in a preheated state into the upper portion of the digester. It has only been possible to practically utilize this suitable circulation on using pumps for propelling the digesting liquid through one or several circulation conduits. been made to make the digesting liquid, directly or indirectly heated, rise upward in a conduit built in the digester, and then move from the top to the bottom in the remaining part of the digester filled with fibrous material, but said tests have not led to any practical results, because by only indirect heating the necessary circulation speed is insufiicient, and, moreover, the formation of incrustation cannot be avoided.

The inventor has found that the above stated suitable circulation digestion with good result and with the known advantages, which a circulation of sulphurous gas involves, may be applied, without using liquid pumps, by supplying to a circulation conduit opening into the top and bottom of the digester, which conduit the fibrous material cannot enter, a certain quantity of sulphurous gas together with the quantity of steam, if any, to be added to the digesting liquid, whereby the gas may be introduced wholly or partly mixed with steam. Said gas or gas mixture, flows upward through the conduit, and thus a suction is effected in the lowest portion of the same.

The circulation of the digesting liquid thus arisen maybe increased by introducing the gas and the gas mixture respectively, and the digesting liquid in such a way that injector'actionarises. The circulation may also be increased in another way, for example by using pumps or compressors. In order to avoid increase of the pressure, gas may be drawn all from the upper portion of the digester to the necessary extent.

In applying the inventors circulation method now stated it is possible to allow the digesting liquid to be heated only by direct supply of steam, mixed with gas, if desired, or to effect the heating of the digesting liquid wholly or partly indirectlyeither in the digester-itself, or in a. preheater in the circulation conduit. In the lastmentioned case the formation of incrustation in the pre- Tests havev heater is counteracted by the excess of sulphurous acid in the digesting liquid.

In applying the inventors said method it is also possible to supply preheated, or not preheated digesting liquid from another digester to the circulation conduit prior to or after introducing the gas and the gas mixture respectively.

The invention comprises also a process for efiecting in the digestion of sulphite cellulose a circulation of the digesting liquid from the top to the bottom through the space filled with fibrous material in the digester, and from the bottom to the top in a conduit opening completely within the digester at the top and the bottom of the digester, sulphurous gas or steam, or a mixture of 7 steam and sulphurous gas being pressed into the conduit, and being mixed with digesting liquid therein under injector action.

Thus a very good circulation of the digesting liquid is obtained with movement from the top to the bottom through the charge of chips without using power consuming pump devices.

Further the invention relates tothe improve ment in digesting sulphite cellulose in a digester having a circulation conduit for the digesting liquid, into which gas, or gas and steam is introduced, by introducing the gas, or the gas and the steam into the digester or the conduit at a height above the bottom of the digester corresponding at least to A preferably to about of the total height of the digester, in order to reduce the resistance to the circulating gas as much as possible.

Further the invention relates to certain means for carrying out the circulation processes in question, more particularly to screens for intro- :ducing the digesting liquid into the circulation conduit, and means for introducing steam, gas, or gas'mixture into the same pipe under injector action. In the accompanying drawings Figure 1 is a partial section of a digester, provided with an interior circulation conduit according to the invention.

Fgure 2 is a detail section along the line 22 of Figure 1 on a larger scale.

Figure 3 is a section along the line 33 of Figure 2.

Figure 4 is a partial vertical section through a digester provided with means for carrying out the processaccording to the invention.

Figures 5, 6 and 7 are details of the apparatus shown in Figure 4 ona larger scale.

Figure 8 is a horizontal section of another means for carrying out the invention.

Figure 9 is a section along the line 9-9 of Figure 8.

1 Figure 10 is a detail of the apparatus shown in Figures 8 and 9 on a largerscale.

Figure 11 is a section along. the line 1111 of Figure 10 on a larger scale.

In Figure 1 20 indicates the digester in which is located a conduit or flue 21 opening at the top and at the bottom into the digester, said conduit at a height above the bottom of the digester corresponding to about A; of the height of the digester being provided with a gas or steam jet' apparatus 22, to which are connected two supply pipes 23, 24 for supplying steam, and a supply pipe 25 for supplying sulphurous gas. The steam in the pipe 23 may preferably have a pressure of about 7 atmospheres, and in the pipe 24 of about 20 atmospheres. The lowest portion of the flue 21 is preferably connected to a screen, device 26 located in the bottom of the digester, through which screen the digesting liquid may be drawn off in the pipe 27 when the digestion is ready. The end of the fine 21 opening into the upper portion of the digester 20 is provided with a screen 28. To said screen is connected a pipe 29 opening into the uppermost portion of the digester, which pipe thus may be said to constitute a continuation of the flue 21f When the digester at the beginning of the digesting process is almost filled with digesting liquid, said continuation has for its object to effect a circulation in the digesting liquid in the uppermost portion of the digester. When later, as the digesting process proceeds, the digesting liquid sinks in the digester, and the pressure round the screen 28 becomes lower, the liquid flowing in the flue will, of course, to a larger extent enter the digester through the screen 28.. In the construction of the upper portion 29 of the circulation pipe it is important to observe that the opening through which the digesting liquid passes from the pipe to the contents of the digester is made large enough so that chips outside the pipe do not check the now too much. Provision should preferably be made that the liquid is allowed to flow downward through one or more annular openings, thus preventing chips from entering the pipe.

In order to prevent steam from entering, and passing through the flue 21 when making the chips basic, a throttle valve 30 is located in the same, which valve is thus held throttled during the basic process. The flue is preferably also are connected to the supply pipes 23'and 24.

Thus each of the canals 32, 33, 34 and 35 is separately connected to the steam supply pipe 23,

and adapted to be shut off by means of valves 36. The high pressure steam from the pipe 24 together with the sulphurous gas enters .from the canal 35. The canals 32, 33 and 34 are connected to the interior of the flue 21 by means of 'upwardly'directed, mamelonated exhaust canals 37. The exhaust canals 38 of the canal 35 are not same temperature.

embodiment of an apparatus, provided with' mamelonated. If desired, the exhaust canals may be provided with removable nozzles. It is clear that the supply pipes to the gas and steam jet apparatus respectively also may be arranged for supply of only sulphurous gas or only steam, and also in such way that the gas does not meet the steam until -in the flue. The steam jet apparatus may also be connected only to a steam supply pipe, and the annular canals may also in another way than as has been shown he connected to the different supply pipes. The work of the steam jet apparatus is considerably facilitated by being placed on the above mentioned height above the bottom of the digester, because the liquid column which offers the greatest resistance to the gas or the steam then becomes relatively small. The conduits for the circulation arethus also to a great extent changed from pressure conduits to suction conduits, and thus the tendency of.

forming gypsum occurring in pressure conduits is considerably reduced.

Further, due to the simple embodiment of the system, one obtains so spacious dimensions of necessary conduits and members for a relatively a smaller specific gravity in the conduit by being so to speak impregnated there by gas and steam. The low speed of the digesting liquid in combination with straight conduits and passages counteracts considerably formation of incrustation on the interior walls of the apparatus.

The disposition of the steam jet apparatus within the digester makes the use. of a straight system possible i. e. a system in which the digesting. liquid is not drawn offfrom the digester to the heating source by means of pumps in order to be returned to the digester-again, but in which the digesting liquid only has to pass through an almost straight pipe. The driving action of the steam jet apparatus develops its highest power first when the temperature exceeds 70 C.; a centrifugal pump loses its suction capacity at the small, almost no parts being outside the digester.

The heat losses are very The system also ofiersa .very great reliability of service and low maintaining costs, no moving parts being at hand.

According to Figures 4, 8 and 9 an annular that kind is difficult to mount and difficult'totake out and drawbacks arise on account of the expansion of the material at raising temperature. The screen devices forming part of the invention are constructed in such a manner that the said drawbacks are removed.

The screen device consists of two conduits in the embodiment shown in Figure 4, said conduits.

being mutually connected to a pipe 39. Each conduit consists of .a number of segments 40 shaped as screen members, said segments being flexibly connected by means of sleeves 41! Said sleeves 41 'are provided with shoulders 42 resting against'the wall of the digester so that the conduit is held at some distance from the wall. The shoulders 42 which rest loosely against the wall tionarily connected to the said sleeve being formed,

of the digester are suitably designed in such a way that the centre of gravity of each screen segment 40 lies in a plane above the upper resting edge of the shoulders so that the conduits whenexpanding due to increased temperature will turn upward and outward about said edge, i. e. in the sense indicated by the arrow in. Figure 7. In order to prevent the conduit from sliding downward the conduit rests against aloutments 44 whichare stationarily connected to a loose continuous ring 45 resting on the bottom of the digester. The abutments 44 may also be stawall of the digester.

The shoulders 42 may also be adapted only to rest against the abutments 44, and the conduits may rest directly with their sleeves against the wall of the digester. The conduits may also communicate with each other by meansiof several pipes 39.

The lower conduit communicates with a. pipe 46 connected by means of cocks partly to the circulation conduit 47, and partly to-an exhaust conduit 48.

The screen segments 40 consist of tube pieces which are preferably bent to flt the shape of the wall of the digester, but they may also be straight. The segments are preferably made of the same size. whereby when mounting the screen device the length of the conduit is simply adjusted after" the width of the superficies of the digester by cutting off the last segment. The shoulders, which also may be located at another place than on the sleeves of the tube pieces, are adjusted after the shape of the digester when mounting the apparatus. The conduit follows the wall of the 'digester very well because the sleeves are designed so that a play exists between the tube pieces and the sleeves, and consequently a certain flexibility of the conduits is obtained.

Figure 5 shows a detail of a conduit in which straight tubes are used. In order to unite two screen segments'a loose sleeve 41 is here used, the with a shoulder adapted to rest against the wall of the digester.

When using bent tube segments (Figure 6) one end is preferably shaped as a sleeve 41 in which the opposite end of the adjacent segment 40 is introduced.

Of course the play between tubes and sleeves the said play effecting the flexibility, must not be so large as to enable fibers to pass through same.

The tubes may either be provided with fine holes and thus act as screens or with larger holes 49 (Figure 3), surrounded by one or more screen members 50, preferably in the form of a cylinder, covering the said holes and formed with a perforated 'superficies, a very large screen face being obtained in the last mentioned case.

Instead of being round the screen device may have other cross section which may be more suit able to effect less resistance against the fibrous mass on emptying the digester. The cross section may for instance beformed as a triangle one side of which rests against the wall of the digester. A suitable embodiment is to arrange such a screen close to the outlet, the cross section of the said screen being of a triangular shape.

The screen device may consist also of one single the lower conical portion of the digester. The

said rings are arranged in such a manner that all liquid entering the upper ring is led to the lower oblong shape and the head ring below the screen face of same, from where it is either led away from the digester or is led to a higher situated place in the same along with liquid flowing through the screen face into the lower ring. The saidscreen rings may consist of segments connected by meansof joints, and may be placed in the brickwork of the digester, the segments of the upper ring being made pointed at their upper ends, so that the brickwork will lie on the same level with the screen faces, which highly facilitates the exhaustion of the pulp.

In the embodiment shown in the Figures 8 and 9 the screen consists partly of an upper ring formed of segments 51, connected with each other and of the same shape, partly of alower ring formed of the segments 52 which are connected with each other and also are of the same shape. The segments are preferably locked by means of bolts and nuts applied in opposite holes of adjacent segments. The bolt is provided with a square portion right below the head of the bolt, the said portion being somewhat thicker than the thickness of the screen plate. the different segments relatively to each other. aration of parts the holes round shape and those of get a certain mobility To facilitate the sepof one segment have a the other segment an of the bolt an oblong shape, the head of the bolt thus being turned that way at the locking that the longitudinal direction of the said head becomes perpendicular to the oblong hole. on separating the parts one need only unfasten the nut and turn the bolt 0n the side facing the interior of the digester each segment is provided with perforations and the said segment is not made larger than can be introduced through the neck opening of thedigester and can be handled by one man without dimculty. Intermediate conduits 53 are placed between the two rings and distributed all around, all liquid entering the upper ring being conducted through the intermediate conduit to the lower ring and therefrom away from the digester through the conduit 54, or during the digestion, in order that digesting liquid shall circulate in the digester, up through the flue 55. The intermediatelconduits may preferably be perforated in order to obtain a larger screen face. The upper ring rests on stages 56 in the brickwork of the digester and the. lowerscreen ring rests against a ring 57 located in the bottom of the digester.-

Canals or recesses for. the intermediate conduits 53 are arranged in the brickwork between the rings. In order to facilitate the exhaustion of the pulp, the interspace between the screen rings is filled with brickwork of such a thickness that it is on the same level with the screen faces. For this purpose also the segments 51 of the upper ring have been made pointed at their upper ends. The segments 52 of the lower ring may also be made pointed at their .upper ends and of course Hereby is obtained that r one need not then fill the interspace between the intermediate conduits may be partly limited by I the wall of the digester so that the same will form the bottom of each segment.

Figures 10 and 11 show how an intermediate conduit 53 may be applied in the brickwork between the rings.

above downwardly through the space of a digester, filled with fibrous material, and from-below upwardly in a conduit, opening at the upper and lower part of the digester and into which conduit the fibrous material is prevented from entering, introducing sulphurous gas into the conduit, sucking the digesting liquid into the lower part of the conduit and pressing out said liquid into the digester from the upper part of the conduit, while leading off suflicient gas from the upper part of the digester to avoid an increase of the pressure.

2. In a process as claimed in claim 1, introducing in the digesting liquid the whole quantity of steam needed into the conduit.

3. In a process as claimed in claim 1, in which the gas is introduced into the conduit mixed with steam.

4. In a process as claimed in claim 1 indirectly heating the digesting liquid while circulating through the conduit outside the digester.-

5. In a process-as claimed in claim 1, introducing digesting liquid from another digester into the circulation conduit.

6. In a processes claimed in claim'l, introducing the gas into the conduit in such a manner that an injector action arises and the circulation of the digesting liquid. is furthered thereby.

7. In a processas claimed in claim 1', introducing the gas along with steam into the conduit in such a manner that an injector action arises and the circulation of the digesting liquid is furthered thereby.

8. A process for digesting sulphite cellulose, consisting in circulating digesting liquid from above downward through the space of the digester filled with fibrous material and from below upward in.a conduit located entirely inside the digester and open at its upper and lower ends into which conduit the fibrous material is prevented from entering, forcing sulphurous gas from a source located outside the digester into the conduit and mixing therewith the digesting liquid under injector action.

V 9. A process for digesting sulphite. cellulose, consisting in" circulating digesting liquid from above downward through the space of the digester, filled with flbrous'material and from below upward in a .conduit located entirely inside the. digester and open at its upper and lower ends into.

which conduit the fibrous material is prevented from entering by forcing a mixture of sulphurous gas and steam from a source located outside the digester into the conduit and mixingtherewith the digesting liquid under injector action.

10. A process for digesting sulphite cellulose, consisting in circulating digesting liquid from above downward through the space of the digester, filled with fibrous material and from below upwardin a conduit located entirely inside the digester and open at its upper and lower ends into which conduit the fibrous material is prevented from entering, forcing partly steam, partly sulphurous gas from a source located outside the digester into the conduit and mixing therewith the digesting liquid under injector action.

11. A process for digesting sulphite cellulose consisting in circulating the digesting liquid together with sulphurous gas mixed with steam from above downward through the space of the digester, filled with a fibrous material, and from below upward in a conduit opening at the upper and the lower ends of the digester, while introducing the gas into the digester at a height above and forcing said liquid into the digester from the upper part 01- the conduit.

13. In combination with a sulphite digester, .a device comprising a circulation conduit which opens at the upper and the lower end of the digester, a jet apparatus formed at a suitable place on the conduit and a plurality of supply pipes leading to the jet apparatus at least one of said supply pipes being connected to a gas injector with inlet for steam, the other supply pipes being connected with supplies for steam and valves on said pipes adapted to close the pipes.

14. A combination with a sulphite digester, a device comprising a circulation conduit which opens at the upper and the lower ends of the digester, a jet apparatus in the shape of a ring enclosing a plurality of superposed canals, which communicate with the supply pipes, at least one of said supply pipes being adapted for a gaseous fluid and from which canals, directed obliquely to vertical exhaust canals, open into the interior of said ring, the ring being at its upper and lower ends connected to the circulation conduit.

15. In combination with a sulphite digester having a circulation conduit opening at the upper and the lower conical ends of the digester, a deother to form several conduits extending around and along the'wall of the digester, the said conduits being connected with each other by means of pipes, and supports for said pipes arranged inside the digester.

16. In combination with a sulphite digester having a circulation conduit opening at the upper end and the lower conical portion of the 'digester, a device comprising a screen element located in said lower conical portion connected to the circulation conduit, consisting of tubular screen segments, ,by means of sleeve joints connected with each other to form at least one conduit'extending around and alongthe wall of the digester, supports arranged inside the digester for said .segments, each screen segment consisting of a perforated tube, a screen member surrounding each tube, preferably in the form or a covering cylinder with a perforated superflcies.

17. In combination with a sulphite digester having a circulation conduit opening at the upper end and the'lower conical portion of the digester, a device comprising a screen element 10- cated in said lower conical portion connected to the circulation "conduit. consisting of tubular screen segments, by means of sleeve joints connected with each other to form at least one conduit extending around and along the wall of the digester, supports arranged inside the digester for said segments, shoulders located on the conduit, the said shoulders resting loosely against the wall of the digester and being shaped in such a manner that the centre of gravity of each screen segment islocated in a plane above the upper resting edge of the shoulders, in order that the conduit, when expanded due .to increased temperature, may be able to turn upward and outward around the said edge.

18. In combination with a sulphite digester having a circulation conduit opening at the upper end and the lower conical end of the digester, a device comprising a screen element located in said lower conical end in the form of two hollow perforated rings one located above the other and arranged in such a manner that all liquid entering the upper ring is led away to the lower ring below the screen face of the same and from there along with the liquid flowing through the screen face into the lower ring leaves through an outlet, connected to the circulation conduit.

- 19. A device as claimed in claim 18, in which a plurality of intermediate conduits are arranged between the upper and lower ring.

, 20. A device as claimed in claim 18; in which said rings consist of segments connected with each other by means of joints.

21. A device as claimed in claim 18, in which each screen ring rests on stages in the wall of the digester.

22. A device as claimed in clam 18, in which at least the upper ring is pointed at its upper end.

23. A device as claimed in claim 18, in which the cross sections of both rings are of an oblong shape and closely follow the wall of the. digester.

24. A device as claimed in claim 18, in which brickwork with canals for the intermediate conduits fills the interspace between the rings.

25. A device as claimed in claim 18, in which the rings are partly limited by the wall of the digester.

SJUNE SVENSSON. 

